Betekhtinite

Formula: Cu10(Fe,Pb)S6

Reflected/transmitted colour: opaque, polished section bright cream parallel to elongation, stronger yellowish cream perpendicular, dulls on exposure

Pleochroism:

Optical isotropy/anisotropy: polished section in air strong anisotropy, //c dark gray-black, c dark yellow-brown and dark blue-green, in oil stronger anisotropic, more vivid colours

Optical sign:

Refractive indices:

Birefringence δ/bireflectance: polished section in air distinct, //c light cream, c more yellow cream, in oil stronger, the colours having a more yellow tinge

2V angle:

Dispersion:

Optical orientation:

Optical axial plane:

 

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